In situ behavioral responses of crustacean zooplankton to an approaching seismic survey.

Abstract

The impacts of underwater noise from seismic surveys on zooplankton remain poorly understood despite their critical ecological role. This study investigated the effects of in situ airgun shots on the swimming behavior of the copepod Calanus finmarchicus at distances from over 4000 to less than 100 m from the seismic airgun array (3060 in³, 50.1 L). Copepods were deployed in a cage equipped with a stereo camera system to track individual swimming behavior. Our findings reveal significant changes in swimming speeds and speed-based behavioral classifications: Swimming, Sinking, and Jumping. During airgun exposure, the swimming speed increased significantly, displaying a quadratic relationship around an airgun shot. More copepods jumped, with higher relative jumping counts per individual, following a non-linear relationship with distance from the seismic source. Sinking duration decreased, while swimming lasted longer during shoot periods. Furthermore, our findings suggest that changes in fluid flow speeds and low-frequency sound induced by airgun shots may have driven some of the observed responses, underscoring the complex interaction between seismic activity and copepod behavior. This study not only sheds light on the behavioral effects of impulsive noise on pelagic copepods but also introduces a novel methodology for field research involving small aquatic organisms.